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A slip assembly for gripping against the external surface of a section of
pipe or other tubular goods and supporting axial loading has multiple
sets of cooperating wedge-like slip members movably mounted within a slip
bowl. A first set of slip members having a smaller taper angle (that is,
having a greater vertical component) exerts a predetermined and limited
radial gripping force on the pipe or other tubular good. Thereafter, a
second set of slip members having a larger taper angle (that is, having a
lesser vertical component) takes over and exerts additional radial
gripping force on the pipe or other tubular good.

Inventors:

LOUVIERE; JEREMY; (BROUSSARD, LA); MEAUX; JAMIE; (BROUSSARD, LA)

Applicant:

Name

City

State

Country

Type

OFFSHORE ENERGY SERVICES, INC.

Lafayette

LA

US

Family ID:

1000002955831

Appl. No.:

15/796978

Filed:

October 30, 2017

Related U.S. Patent Documents

Application Number

Filing Date

Patent Number

14208051

Mar 13, 2014

9803435

15796978

61792038

Mar 15, 2013

Current U.S. Class:

1/1

Current CPC Class:

E21B 19/10 20130101

International Class:

E21B 19/10 20060101 E21B019/10

Claims

1. A method for gripping pipe and other tubulars comprising: a) inserting
a section of pipe in a slip assembly, said slip assembly comprising: i) a
slip bowl member having a central bore defining a tapered inner bowl
surface; ii) a first slip member having first tapered inner slip surface,
a first tapered outer slip surface, and at least one substantially
upwardly facing shoulder on said first tapered inner slip surface,
wherein said first tapered outer slip surface is slidably disposed on
said inner bowl surface; iii) a second slip member having a second inner
slip surface, a second tapered outer slip surface and at least one
substantially downwardly facing shoulder on said second tapered outer
slip surface, wherein said second tapered outer slip surface of said
second slip member is slidably disposed on said first tapered inner slip
surface of said first slip member; iv) at least one die member disposed
on said second inner slip surface of said second slip member; b) engaging
said second slip member against said pipe section and said first inner
slip surface of said first slip member; c) engaging said downwardly
facing shoulder against said upwardly facing shoulder when pipe gripping
force exerted by said second slip member on said pipe section exceeds a
predetermined force; and d) engaging said first slip member against said
first tapered inner bowl surface of said slip bowl.

2. The method of claim 1, wherein said outer surface of said first slip
member defines a first acute angle from a longitudinal axis of said
section of pipe, said inner surface of said first slip member and said
outer surface of said second slip member define a second acute angle from
the longitudinal axis of said pipe section, and said first acute angle is
larger than said second acute angle.

3. The method of claim 1, further comprising a gap between said upwardly
and downwardly facing shoulders when said pipe gripping force exerted by
said second slip member on said pipe section is less than said
predetermined force.

4. The method of claim 1, wherein the size of said gap between said
upwardly and downwardly facing shoulders is adjustable.

5. The method of claim 1, further comprising a bias spring disposed
between said first and second slip members, wherein said bias spring is
configured to create a gap between said upwardly and downwardly facing
shoulders.

6. A method for gripping pipe and other tubulars comprising: a) inserting
a section of pipe in a slip assembly, said slip assembly comprising: i) a
slip bowl member having a central bore defining a first tapered inner
bowl surface; ii) a first plurality of slip members, each having an inner
surface, an outer surface, and at least one substantially upwardly facing
shoulder on said inner surface, wherein said outer surfaces of said first
plurality of slip members are slidably disposed on said tapered inner
bowl surface and said inner surfaces of said first plurality of slip
members cooperate to define a second tapered bowl surface; iii) a second
plurality of slip members, each having an inner surface, an outer surface
and at least one substantially downwardly facing shoulder on said outer
surface, wherein said outer surfaces of said second plurality of slip
members are slidably disposed on said second tapered bowl surface defined
by said inner surfaces of said first plurality slip members; iv) a
plurality of die members disposed on said inner surfaces of said second
plurality of slip members; b) engaging said second plurality of slip
members against said pipe section and said inner surfaces of said first
plurality of slip members, wherein said second plurality of slip members
are axially displaced relative to said first plurality of slip members;
c) engaging said downwardly facing shoulders of said second plurality of
slip members against said upwardly facing shoulders of said first
plurality of slip members when axial displacement of said second
plurality of slip members reaches a predetermined distance; and d)
engaging said first plurality of slip members against said first tapered
inner bowl surface of said slip bowl.

7. The method of claim 6, wherein said outer surfaces of said first
plurality of slip members define a first acute angle from a longitudinal
axis of said section of pipe, said inner surfaces of said first plurality
of slip members and said outer surfaces of said second plurality of slip
members define a second acute angle from the longitudinal axis of said
pipe section, and said first acute angle is larger than said second acute
angle.

8. The method of claim 6, further comprising a gap between said upwardly
and downwardly facing shoulders when said when axial displacement of said
second plurality of slip members has not reached said predetermined
distance.

9. The method of claim 6, wherein the size of said gap between said
upwardly and downwardly facing shoulders is adjustable.

10. The method of claim 6, further comprising a bias spring disposed
between said first plurality and second plurality of slip members,
wherein said bias spring is configured to create a gap between said
upwardly and downwardly facing shoulders.

Description

CROSS REFERENCES TO RELATED APPLICATION

[0001] THIS APPLICATION IS A CONTINUATION OF UNITED STATES NON-PROVISIONAL
PATENT APPLICATION NO. 14/208,051, FILED MAR. 13, 2014, CURRENTLY
PENDING, WHICH CLAIMS PRORITY OF UNITED STATES PROVISIONAL PATENT
APPLICATION SERIAL NO. 61/792,038, FILED MAR. 15, 2013, ALL INCORPORATED
HEREIN BY REFERENCE.

STATEMENTS AS TO THE RIGHTS TO THE INVENTION MADE UNDER FEDERALLY
SPONSORED RESEARCH AND DEVELOPMENT: NONE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention pertains to a slip assembly for gripping pipe
and other tubular goods. More particularly, the present invention
pertains to a slip assembly for gripping heavy weight pipe and other
tubular goods, while reducing or eliminating damage to exterior surfaces
of such pipe and/or tubular goods.

2. Brief Description of the Prior Art

[0003] Conventional drilling rigs typically comprise a supportive rig
floor, a substantially vertical derrick extending above said rig floor,
and a traveling block or other hoisting mechanism which can be raised and
lowered within said derrick. In addition to other tasks, such equipment
can be used to insert and remove pipe and other tubular goods from a
wellbore situated below said rig floor and derrick.

[0004] During pipe installation operations, pipe is typically inserted
into a well in a number of different sections of roughly equal length.
These sections, often called "joints," are typically screwed together or
otherwise joined end-to-end at a drilling rig in order to form a roughly
continuous "string" of pipe that extends into said wellbore. As the
bottom end of the pipe string penetrates deeper into a wellbore,
additional joints of pipe are added to the ever lengthening pipe string
at the drilling rig. Conversely, when a pipe string is being removed from
a wellbore, the upper portion of said pipe string is pulled from the well
and one or more joints are unscrewed in the rig derrick until a desired
length of pipe has been retrieved from said well.

[0005] The process of inserting a string of pipe in a well is typically
commenced by lowering a first section of pipe into a wellbore at the rig
floor, and suspending said section of pipe in place using a set of "lower
slips." When set, such lower slips--also sometimes referred to as "spider
slips"--generally surround an opening in the rig floor (which is aligned
with the upper opening of said well) through which the upper end of said
first section of pipe protrudes. The lower slips grip against the
external surface of said pipe section and hold such pipe in place.

[0006] Thereafter, a second section of pipe is lifted within the drilling
rig derrick and suspended in said derrick from the rig's traveling block,
top drive unit or other hoisting mechanism. Said second section of pipe
is then positioned in axial alignment above the first section of pipe
which was previously run into the well and suspended from the lower
slips. The lower end of said second pipe section is then connected to the
upper end of said first pipe section.

[0007] Once said pipe sections are joined, the pipe string can be
suspended from the rig's traveling block (or top drive unit or other
hoisting mechanism), allowing the total weight of said pipe string to be
suspended within the derrick. In the position, the lower slips can be
disengaged from gripping the pipe. The joined sections of pipe can then
be lowered further into the wellbore using the rig's traveling block, top
drive unit or other hoisting mechanism. After the pipe string has been
lowered a desired length within the wellbore, said lower slips can again
be engaged to grip the pipe string and hang it in place within said
wellbore. Thereafter, the process can be repeated until a desired length
of pipe has been inserted into the well.

[0008] Conventional slip assemblies (including, without limitation, lower
or "spider" slip assemblies) typically utilize a plurality of
wedge-shaped slip members, movably disposed within a bowl-like structure,
in order to selectively grip against the outer surface of pipe and/or
other tubular members. Each such slip member typically has a
substantially vertical surface and a tapered back side. Although the
angle of such taper can vary, conventional slip members typically have a
taper angle of 9.46 degrees. The substantially vertical surface has
gripping teeth or "dies" and is oriented inwardly toward the pipe or
other tubular member, while the tapered back side is oriented facing away
from such pipe or other tubular member and is slidably mounted in said
slip bowl. The inwardly facing gripping surface can also have an arcuate
shape that conforms to the outer surface of a section of pipe or other
tubular to be gripped.

[0009] When pipe is gripped by a slip assembly, the tapered outer surfaces
of the slip members, in cooperation with the corresponding tapered inner
surface of a slip bowl in which such slip members are received, force
said slip members radially inward around the outer surface of the pipe.
Such slip members essentially wedge between the slip bowl and the pipe,
thereby causing said slip members to grip against the outer surface of
the pipe. As a result, the greater the axial load acting on said slip
members, the greater the radial gripping force that said slip members
impart on said pipe.

[0010] Designing of slip assemblies in general, and slip members in
particular, can be very challenging. Generally, the greater the taper
angle of such slip members, the lower the radial force that said slip
members impart on pipe. Conversely, the lower the taper angle of such
slip members, the greater the radial force that said slip members
generally impart on pipe. Thus, if a slip taper angle is too large, the
slip members will not create enough radial force to grip against the
outer surface of the pipe. However, if a slip taper angle is too small,
such slip members may impart too much radial force on pipe, thereby
damaging the outer surface of such pipe and, in extreme cases, causing
such pipe to collapse or crush.

[0011] Slip assembly design is further complicated by changes in pipe and
other tubular goods used in modern wells. As wells are being drilled to
deeper depths and/or in more challenging environments, pipe and other
tubular goods used to service and equip such wells is evolving. For
example, casing used in such wells is often larger and/or heavier than
casing used in other wells. Further, casing, production tubing and/or
other tubular goods are often constructed of and/or coated with premium
materials that are less rugged and more easily damaged than conventional
tubular materials. Care must be taken that slip members do not damage
such pipe and/or other tubular goods including, without limitation, as a
result of excessive radial gripping forces.

[0012] Conventional slip assemblies have proven to suffer from some
significant limitations. Under extreme loading conditions, conventional
slip assemblies can cause a crushing effect that can damage pipe and
other tubular goods gripped by such slip assemblies. This crushing effect
can be lessened by increasing the taper angle of slip members and a
cooperating slip bowl. However, when this angle is increased, the slip
members may have difficultly engaging against and gripping a section of
pipe, especially when such slip members must engage against a relatively
light load (such as, for example, when relatively few pipe sections are
joined to a pipe string).

[0013] Thus, there is a need for a slip assembly that can be used to grip
and convey heavy weight pipe and/or other tubular goods, such as casing,
during installation and retrieval operations. Such slip assembly should
be capable of generating sufficient radial force to securely grip heavy
weight pipe and other tubular goods, while preventing crushing and/or
damage to the external surfaces of such pipe and tubular goods.

SUMMARY OF THE INVENTION

[0014] The slip assembly of the present invention comprises a plurality of
slip members that cooperate to grip against the outer surface of a
section of pipe. Although multiple different applications can be
envisioned without departing from or limiting the scope of the present
invention, said slip assembly is described herein primarily in connection
with a set of lower "spider" slips. Notwithstanding the foregoing, it is
to be observed that the slip assembly of the present invention can be
beneficially used in connection with many different uses and/or
applications.

[0015] The slip assembly of the present invention comprises a slip bowl
member having a central bore for receiving a section of pipe or other
tubular, and defining a generally arcuate inner surface substantially
surrounding said bore. Said inner surface is generally disposed at an
acute angle relative to the central longitudinal axis of said bore,
wherein the diameter of said bore is greater at the top of said bore than
at the base of said bore. A plurality of central slip members is movably
disposed within said bore of said bowl member.

[0016] Said central slip members have a substantially wedge-shaped or
tapered contour profile; each of said central slip members is wider at
its top than at its bottom. Each of said central slip members further
defines an inwardly-facing and generally arcuate inner surface and an
outwardly-facing and generally arcuate outer surface. The outer surface
of each central slip member is slidably disposed on the cooperating inner
surface of said slip bowl bore, while the inner surface of each central
slip member defines an angled surface having at least one upwardly facing
shoulder member.

[0017] The inner and outer surfaces of said central slip members are each
disposed at acute angles relative to the central longitudinal axis of
said slip bowl bore. In a preferred embodiment, the angle of said inner
surface (relative to the central longitudinal axis of said slip bowl
bore) is less than the angle of said outer surface (relative to the
central longitudinal axis of said slip bowl bore).

[0018] A supplementary slip member is moveably disposed on the inner
surface of each central slip member. Said supplementary slip members each
have a substantially wedge-shaped or tapered contour profile; each of
said supplementary slip members is wider at its top than at its bottom.
Said supplementary slip members each define a generally arcuate
inwardly-facing inner surface, as well as a generally arcuate
outwardly-facing outer surface having at least one downwardly facing
shoulder member. Said inner surfaces of said supplemental slip members
are each oriented substantially parallel to the central longitudinal axis
of said slip bowl bore, while said outer surfaces are each oriented at an
acute angle relative to said axis. The outer surface of each
supplementary slip member is slidably disposed on a cooperating inner
surface of a corresponding central slip member.

[0019] Insert dies having a plurality of teeth-like projections are
disposed along the inner surfaces of said supplemental slip members. Said
insert dies have generally arcuate faces which beneficially have similar
curvature to the outer surface of pipe or tubular goods to be gripped by
said insert dies. Alternatively, said insert dies can optionally have
substantially flat faces with little or no arcuate curvature, which may
be more effective when used with certain types or sizes of pipe.

[0020] When the slip assembly of the present invention is used to grip
against the external surface of a pipe section or other tubular, said
supplemental slip members will first engage against said pipe or tubular.
Said supplemental slip members are oriented at a smaller (that is, more
vertical) slip angle than said central slip members. As a result, said
supplemental slip members will exert sufficient radial force on said pipe
so that said pipe will not slip, even at lower string weights.

[0021] Although the more aggressive vertical slip angle of said
supplemental slip members could ordinarily cause pipe crushing or other
damage, said supplemental slip members have a limited (but adjustable)
axial travel distance. As a result, the teeth-like projections of said
insert dies are permitted to penetrate the outer surface of a pipe
section only a predetermined amount. In a preferred embodiment, said
teeth-like projections generate a sufficient friction factor (typically
over 1), even when debris or foreign material (for example, mill scale,
pipe dope or drilling mud) is on the outer surface of such pipe, to
securely grip said pipe. At this point, a less aggressive (that is, more
horizontal) slip angle of said central slip members takes over, ensuring
that radial loads will not increase as fast as pipe weight increases and
minimizing the crushing effect of such slip members. Slip angles of 15
degrees or more, and the benefits associated with such higher slip
angles, are possible as a result of the present invention.

[0022] The slip assembly of the present invention automatically transfers
from the more aggressive slip angle of the supplemental slip members to
the less aggressive slip angle of the central slip members. Thus, no
interaction from an operator is required, thereby reducing the risk
associated with human error. A bias spring can be used to reset the slip
members after pipe is released, thereby readying said slip members for a
subsequent section of pipe.

[0023] A slip set indication assembly can provide a signal that the slip
members of the present invention have reached a fully engaged position.
Such signal allows confirmation that said slip members have fully engaged
against pipe, and are not partially engaged (for example, due to debris
inadvertently wedging around said pipe and/or between said slip members).
The present invention has a large gripping range so multiple pipe
diameters can be accommodated without significant changing of parts or
other equipment in the field.

BRIEF DESCRIPTION OF DRAWINGS/FIGURES

[0024] The foregoing summary, as well as any detailed description of the
preferred embodiments, is better understood when read in conjunction with
the drawings and figures contained herein. For the purpose of
illustrating the invention, the drawings and figures show certain
preferred embodiments. It is understood, however, that the invention is
not limited to the specific methods and devices disclosed in such
drawings or figures.

[0025] FIG. 1 depicts a side sectional view of a section of pipe being
gripped by the slip assembly of the present invention.

[0026] FIG. 2 depicts an exploded perspective view of slip members and
insert dies of the present invention.

[0027] FIG. 3 depicts a top view of assembled slip members and insert dies
of the present invention.

[0028] FIG. 4 depicts a side view of assembled slip members and insert
dies of the present invention.

[0029] FIG. 5 depicts a side sectional view of assembled slip members and
insert dies of the present invention along line 5-5 in FIG. 3.

[0030] FIG. 6 depicts a detailed view of the highlighted area depicted in
FIG. 4.

[0032] FIG. 1 depicts a side sectional view of a pipe section 200 being
gripped by slip assembly 100 of the present invention. As depicted in
FIG. 1 and as described herein, slip assembly 100 comprises a set of
"lower slips" or "spider slips" that are generally disposed surrounding
an opening in a rig floor that is substantially aligned with the upper
opening of a well. Notwithstanding the foregoing, it is to be observed
that the slip assembly of the present invention can be utilized in
connection with other pipe gripping uses or applications (other than
lower spider slips) without departing from the scope of the present
invention. Generally, slip assembly 100 of the present invention
comprises a plurality of slip members, as more fully described herein,
that cooperate to selectively grip against the outer surface of pipe
section 200.

[0033] Slip assembly 100 of the present invention comprises a slip bowl
member 10 having a body member 11 with a central bore 12 extending
therethrough for receiving a section of pipe or other tubular (such as
pipe section 200), and defining a generally arcuate inner surface 13.
Said inner surface 13 is generally disposed at an acute angle relative to
the central longitudinal axis of bore 12 (and pipe section 200).
Accordingly, the diameter of bore 12 is greater at its upper end than at
its lower end. Although not depicted in FIG. 1, a plurality of elongate
keyway slots extend along at least a portion of said bore 12.

[0034] Still referring to FIG. 1, a plurality of central slip members 20
are slidably disposed within bore 12 of slip bowl assembly 10. Said
central slip members 20 have a substantially tapered contour profile,
wherein each of said central slip members 20 is wider at its top 27 than
at its bottom 28. Each of said central slip members 20 further defines an
inwardly-facing inner surface 21 and an outwardly-facing outer surface 25
that is generally shaped to conform to inner surface 13 of bore 12 of
slip bowl member 10. Outer surface 25 of each central slip member 20 is
slidably disposed on cooperating inner surface 13 of slip bowl 10. Said
inner surface 21 of each central slip member 20 defines an angled surface
having at least one upwardly facing shoulder member 22.

[0035] A supplementary slip member 30 is moveably disposed on inner
surface 21 of each central slip member 20. Said supplementary slip
members 30 each have a substantially wedge-shaped or tapered contour
profile; each of said supplementary slip members is wider at its top 37
than at its bottom 38. Said supplementary slip members each define an
inwardly-facing inner surface 31, as well as outwardly-facing outer
surface 35 having at least one downwardly facing shoulder member 36.
Insert die assemblies 40 having a plurality of teeth-like projections are
disposed along the inner surfaces 31 of said supplemental slip members
30. Said insert die assemblies 40 have generally arcuate inner surfaces
which beneficially have similar curvature to the outer surface of pipe
section 200. Alternatively, said insert die assemblies 40 can optionally
have substantially flat faces with little or no arcuate curvature, which
may be more effective when used with certain types or sizes of pipe.

[0036] FIG. 2 depicts an exploded perspective view of a central slip
member 20, supplemental slip member 30 and an insert die assembly 40 of
the present invention. Said central slip member 20 has a substantially
tapered contour profile defining an inwardly-facing inner surface 21 and
an outwardly-facing outer surface 25. At least one alignment key member
26 extends from said outer surface 25. As depicted in FIG. 1, outer
surface 25 of each central slip member 20 is slidably disposed on
cooperating inner surface 13 of slip bowl 10; although not shown in FIG.
1, said alignment key 26 can be slidably received within a keyway slot
extending along said inner surface 13 of bore 12 of slip bowl 10 to
secure said central slip members 25 against lateral movement within said
bore 12.

[0037] Inner surface 21 of central slip member 20 defines an angled
surface having upwardly facing shoulder members 22, as well as a recess
or void 23 extending into the body of said central slip member 20.
Threaded bore 24 extends from the upper surface of said central slip
member 20 into recess 23. Adjustment bolt 60 and bias spring 70 are
received within said threaded bore 24 as described in more detail below.

[0038] As noted above, supplementary slip member 30 is moveably disposed
on inner surface 21 of central slip member 20. Supplementary slip member
30 has a substantially wedge-shaped or tapered contour profile defining
inner surface 31and outer surface 35 having downwardly facing shoulder
members 36. Biasing member 39 extends from said outer surface 35 of
supplementary slip member 30 and is generally aligned with recess 23 in
inner surface 21 of central slip member 20. Although not visible in FIG.
2, said biasing member 29 has a bore extending through said biasing
member.

[0039] In a preferred embodiment, inner surface 31 has a plurality of
beneficially arranged die carrier projections 32 and a central elongate
slot 33 for mounting insert die assemblies 40. Insert die assemblies 40
comprise die carriers 43 having rear wedge projections 44. Said rear
wedge projections 44 are beneficially arranged to engage in mating
relationship between die carrier projections 32 of supplemental slip
member 30. Locking rod 52 can be received within central elongate slot 33
and secured in place to prevent lateral movement of said die carriers 43
relative to supplemental slip member 30. In a preferred embodiment, said
locking rod 52 can be secured in place using locking plate 50 having
bores 53 extending there through; locking plate 50 is removably anchored
to supplemental slip member 30 using locking bolts 51 that extend through
bores 53 and are secured in threaded bores 34.

[0040] Insert die assemblies 40 each further comprise die members 41
having a plurality of inwardly facing teeth-like projections 42. Said
insert die members 41 are disposed along the inner surfaces of said die
carriers 43 and can have generally arcuate inner surfaces which
beneficially have similar curvature to the outer surface of a pipe or
tubular to be gripped by slip assembly 100 of the present invention (such
as, for example, pipe section 200 depicted in FIG. 1). Alternatively,
said insert dies can optionally have substantially flat faces with little
or no arcuate curvature, which may be more effective when used with
certain types or sizes of pipe.

[0041] Referring to FIG. 1, inner surface 21 and outer surface 25 of each
central slip member 20 are disposed at acute angles relative to the
central longitudinal axis of slip bowl bore 12 and pipe section 200; in
most operational installations, including the configuration of slip
assembly 100 depicted in FIG. 1, the central longitudinal axis of slip
bowl bore 12 and pipe section 200 are both oriented in a substantially
vertical direction. In a preferred embodiment, the angle formed by said
inner surface 21 and said vertical axis is less than the angle formed by
outer surface 25 and said vertical axis.

[0042] Similarly, outer surface 35 of each supplemental slip member 30 is
also disposed at an acute angle relative to the central longitudinal axis
of slip bowl bore 12 and pipe section 200 (vertical axis depicted in FIG.
1); such acute angle is substantially the same as the acute angle formed
by said vertical axis and inner surface 21 of central slip member 20. By
contrast, surface 31 of each supplemental slip member 30 is oriented
substantially parallel to the central longitudinal axis of slip bowl bore
12 and pipe section 200 (vertical axis depicted in FIG. 1).

[0043] FIG. 3 depicts a top view of an assembled central slip member 20,
supplemental slip member 30 and insert die assembly 40 of the present
invention. As discussed above, said central slip member 20 has a
substantially tapered contour profile defining outwardly-facing outer
surface 25 having at least one alignment key member 26 extending from
said outer surface 25. Outer surface 35 of supplementary slip member 30
is moveably mounted against inner surface 21 of central slip member 20.
Insert die assembly 40, comprising die member 41 having a plurality of
inwardly facing teeth-like projections 42, is attached to supplemental
slip member 30 and secured in place using locking plate 50 and locking
bolts 51.

[0044] FIG. 4 depicts a side view of an assembled central slip member 20,
supplemental slip member 30 and insert die assemblies 40 of the present
invention. Central slip member 20 has a substantially tapered contour
profile defining outwardly-facing outer surface 25 and inner surface 21,
as well as protruding alignment key member 26 extending from said outer
surface 25. Outer surface 35 of supplementary slip member 30 is moveably
mounted on inner surface 21 of central slip member 20.

[0045] Inner surface 31 of supplemental slip member 30 has a plurality of
beneficially arranged die carrier projections 32. Rear wedge projections
44 of die carriers 43 are beneficially arranged to engage in mating
relationship between said die carrier projections 32 of supplemental slip
member 30. Locking plate 50 is anchored to supplemental slip member 30
(using locking bolts 51 not visible in FIG. 4). Insert die members 41,
each having a plurality of inwardly facing teeth-like projections 42, are
disposed along the inner surfaces of die carriers 43.

[0046] FIG. 5 depicts a side sectional view of assembled slip members and
insert die assemblies of the present invention along line 5-5 in FIG. 3.
Central slip member 20 has a substantially tapered contour profile
defining outwardly-facing outer surface 25 having protruding alignment
key member 26 extending from said outer surface 25. Outer surface 35 of
supplementary slip member 30 is moveably mounted against inner surface 21
of central slip member 20.

[0047] Biasing member 39 extends from said outer surface 35 of
supplementary slip member 30 and is received within recess 23 in inner
surface 21 of central slip member 20. Bias spring 70 is disposed below
said biasing member 39 within said threaded bore 24, while bolt 60 having
external threads 61 is received within said threaded bore 24 and extends
through bore 39a in said biasing member 39, as well as bias spring 70.
Insert die assemblies 40 are disposed on inner surface 31 of supplemental
slip member 30. Locking rod 52 is received between supplemental slip
member 30 and insert die members 40 and is secured in place using locking
plate 50 which is anchored to supplemental slip member 30 using locking
bolts 51 in threaded bores 34.

[0048] Referring to FIG. 1, when slip assembly 100 of the present
invention is used to grip against the external surface of pipe section
200, supplemental slip members 30 will first engage against said pipe
section 200. As noted above, said supplemental slip members 30 are
oriented at a smaller slip angle (that is, a slip angle having a larger
vertical component) than central slip members 20. Said supplemental slip
members 30 cooperate to exert sufficient radial force on said pipe
section 200 so that said pipe section 200 will not slip or fall in an
axial direction, even at lower string weights.

[0049] Although the more aggressive vertical slip angle of supplemental
slip members 30 could ordinarily crush or otherwise damage pipe section
200, said supplemental slip members 30 have a limited axial travel
distance. Specially, as depicted in FIG. 7, as outer surface 31 of a
supplemental slip member 30 slidably moves along the inner surface 21 of
central slip member 20, downwardly-facing shoulder(s) 36 of said
supplemental slip member 30 moves toward upwardly-facing shoulder(s) 22
of central slip member 20. As depicted in FIG. 6, eventually said
downwardly-facing shoulder(s) 36 of said supplemental slip member 30
bottom out against upwardly-facing shoulder(s) 22 of central slip member
20.

[0050] Referring to FIG. 5, threaded bolt 60 can be adjusted within
threaded bore 24. When said threaded bolt 60 is unscrewed relative to
said threaded bore 24, bias spring 70 acts to direct supplemental slip
member 30 upward relative to central slip member 20. As such,
downwardly-facing shoulder(s) 36 of said supplemental slip member 30
separate or form a gap relative to opposing upwardly-facing shoulder(s)
22 of central slip member 20 (see FIG. 7). In this manner, the travel
distance between said opposing shoulders can be adjusted, thereby
accommodating pipe having different sizes and/or specifications.

[0051] Because downward movement of supplemental slip members 30 is
limited, inward radial movement of insert die assemblies 40 is likewise
limited. As a result, teeth 42 of insert die assemblies 40 are permitted
to penetrate the outer surface of pipe section 200 only a predetermined
amount. In a preferred embodiment, said teeth 42 generate a sufficient
friction factor (typically over 1) against pipe section 200, even when
debris or foreign material (for example, mill scale, pipe dope or
drilling mud) is on the outer surface of such pipe, in order to securely
grip said pipe section 200.

[0052] After downwardly-facing shoulder(s) 36 of said supplemental slip
member 30 bottom out against upwardly-facing shoulder(s) 22 of central
slip member 20, the less aggressive slip angle (that is, a slip angle
having a larger horizontal component) of said central slip members 20
acting against inner surface 13 of slip bowl assembly 10 take over. As a
result, this less aggressive angle ensures that radial loading will not
increase as quickly as pipe weight or other axial loading increases,
thereby minimizing the crushing effect of such combined slip members on
pipe section 200.

[0053] Slip assembly 100 of the present invention automatically transfers
from the more aggressive (more vertical) slip angle of the supplemental
slip members 30 to the less aggressive (more horizontal) slip angle of
the central slip members 20. Thus, no interaction from an operator is
required, thereby reducing the risk associated with human error. Slip
assembly 100 of the present invention has a large gripping range so
multiple pipe diameters can be accommodated without significant changing
of parts or other equipment in the field.

[0054] Additionally, angled outer surface 25 of central slip member is
substantially flat. Conventional slip and bowl assemblies typically
include a cone member machined into a bowl and a matching cone member
machined onto a corresponding slip member segment. Such a design is
adequate when only a single pipe size is gripped with each slip
configuration because the taper of the slip and the bowl match exactly
when it contacts the pipe keeping the die contact on the pipe vertical,
and distributing the load into the pipe evenly.

[0055] Slip assemblies exist that can grip multiple pipe diameters without
changing slip inserts. However, such assemblies are generally not
compatible with such conventional cone designs. If slip members do not
sit in a bowl at a machined position, the back of each slip member
segment will only be supported in the center not on the sides--or,
alternatively, only on the outside edges and not in the center.

[0056] By contrast, the slip assembly of the present invention comprises a
substantially flat back side along with a mating substantially flat
surface on the inner surface of slip bowl assembly, thereby permitting a
uniformly distributed load on the back of each slip member throughout the
gripping range of the slip member, insuring a more uniform contact on
pipe and minimizing any pinching or stress concentration areas.

[0057] The above-described invention has a number of particular features
that should preferably be employed in combination, although each is
useful separately without departure from the scope of the invention.
While the preferred embodiment of the present invention is shown and
described herein, it will be understood that the invention may be
embodied otherwise than herein specifically illustrated or described, and
that certain changes in form and arrangement of parts and the specific
manner of practicing the invention may be made within the underlying idea
or principles of the invention.